Cartridge case head structure



Nov. 2, 1965 MAYER ETAL 3,215,077

CARTRIDGE CASE HEAD STRUCTURE Filed March 9, 1964 3 Sheets-Sheet 1 CHARLES E. M/LLER ATTORNEY [I6 2 ALFRED fi /$25 I Nov. 2, 1965 A. A. MAYER Em. 3,215,017

1 gg/ ee 32 1% -45 Am 43 36" I 1 llll iii Nov. 2, 1965 A. A. MAYER ETAL 3,215,077

CARTRIDGE CASE HEAD STRUCTURE Filed March 9, 1964 3 Sheets-Sheet 5 VENTORS F/PE MA YEP RLES E M/LLER BY A 7' TORNE V United States Patent Ofl'ice 3,215,077 CARTRIDGE CASE HEAD STRUCTURE Alfred A. Mayer, West Haven, and Charles E. Miller, Hamden, Cnn., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Mar. 9, 1964, Ser. No. 350,427 Claims. '(Cl. 102-44) The present invention relates to ammunition and more specifically to the construction of a cartridge case made largely of resinous plastic such as polyethylene and acting against the escape of gas around the primer.

Because of the deformability of plastic materials, mounting and gas sealing of the primer is a problem which must be properly solved to provide an acceptable shell.

A mounting and a sealing stem is provided at the base of the shell within an annular groove and has not only a circular hole for receiving the primer but also the stem includes a terminal flap of thick tension ring construction formed integrally as an extension of the stem. Around the primer the ring and stem are taut to prevent entry of gas between the primer and the plastic material of the head. It was found that such a sealing contraction was effective in providing the longest sealing path and snug fit from the very beginning to the completion of shell firing.

The end construction of the stem involves an enlargement extending beyond the end of the primer so as to overlie at least the periphery of the inner end of the primer. Preferably, this plastic primer stem is made so as to be held taut against the side and front edge of the primer. It is preferred that in this primer-surrounding stem the plastic material be not only in circumferential tension but also in slight longitudinal tension intermediate the ends so as to better hold the enlarged extension against the end of the primer. Also, an overlying pressure responsive lip is preferred, pressed down against the inner end of the primer around the flash opening but spaced outward from this opening at the front end of the primer.

Examples of a few preferred ways of realizing the invention are shown in the drawing in which:

FIG. 1 is a longitudinal view in cross section showing part of one shotshell being formed at the integral plastic base according to this invention but shown prior to inset tion of the primer;

FIG. 2 is a view similar to FIG. 1 showing the finished cartridge case including a metal head and with the primer inserted;

FIG. 3 is a longitudinal view in cross section showing a second embodiment in a stage of formation similar to FIG. 1;

FIG. 4 is a partial longitudinal cross section showing another embodiment of finished base of a shell;

FIG. 5 is a fragmentary view taken in cross section at the primer showing a third embodiment; and

FIGS. 6 and 7 show a still further embodiment.

In FIG. 1 the shell body 1 is made of plastic material such as linear high density polyethylene providing a tubular sidewall 2 and a thickened end integral with the sidewall to form a base 3 having the primer opening 4 centered inwardly from a circular channel or internal groove 5 separated from the primer opening by the stem 6 which goes all around the primer opening and has a thickened ring 7 forming an integral extension of the stem projecting beyond the inner extremity of the primer. In this embodiment the inner surface of the opening is made conical by the action of the seal forming punch 21 and the tapered center pin 22 carried by the supporting bunter 23, to provide greater contraction at the inner end of the 3,215,077 Patented Nov. 2, 1965 stem which is put under more hoop tension when the cylindric-walled primer is in place.

Groove 5 is formed by indentation of the plastic in base 3. The stem extension is formed by extrusion up into bore 24 of punch 21 as its stepped end at the annular indenting ridge 25 approaches pin 22.

The extension of the stem is in effect a ring 7 connected by a thin pressure-responsive neck 8 to the rest of the side sealing stem. The end ring also includes an inwardly extending overlapping lip 9 initially disposed at a reverse angle.

When the primer 10 is in place as shown in FIG. 2, lip 9 fits snugly about the inner end of the primer but is spaced sufiiciently from the primer flash hole 11 to avoid being burned away during shell firing. The end ring 7 is made taut against the peripheral radius 12, which is usual around the inner extremity of the primer.

Upon withdrawal of pin 22 the base 3 is next confined in a metal head 13 and the primer then inserted. During insertion of primer 10, the stem end ring 7 is finally formed against punch 21 in bore 24 to the triangular shape shown in FIG. 2 to fit against the primer without a gap.

Thin neck 8 is under both axial and hoop tension since it is under a pull from both the root of the stem and the contracting ring at the crest of the stem protruding beyond the primer.

According to FIG. 3, another embodiment is made using sealing punch 31 having an annular indenting ridge 32 with a conical inner wall and a curling groove and lip adjacent the punch bore 33 which receives the cylindrical end 34 of a forming pin 35 having a tapered and enlarged base portion 36. This with end 34 forms a sharply re cessed shoulder 37 around the pin for coacting, with the curling groove and lip of the punch, upon the plastic material at the stem 46, to indent it at 45 and compressively form it at the primer opening with an internal taper and an O-ring 47 with an internal thick flap 49. The O- ring has pressure-responsive thin connection 48 to the stem at its distal end, i.e. adjacent its crest occupied by the O- ring.

In this embodiment the finished shell 41 is shown in FIG. 4 with the pun-ch 31 and pin 35 removed and the primer 10 inserted in the base 43 provided with a groove 45 and metal head 13 as before. In this embodiment the enlargement at the end of the stem provides the greatest end sealing contraction with most resistance to malformation by the gas and heat encountered.

Theembodiment of FIG. 5, like that of FIG. 4, is made by indentation and compressive reformation of linear high density polyethylene, or the like, similar to the way shown in FIG. 3.

In the embodiment of FIG. 5, the primer 10 is emplaced through the metal head 13 into the plastic base 53 and is fitted under tension in the .stem 56, which extends surrounded by the groove 55. Like the embodiment of FIG. 4, the stem terminates in an enlarged ring 57 thickest at its internal edge forming an aperture leading from the primer flash hole 11 into the powder cavity. In FIG. 5, stem 56 differs in that the thin section 58 is displaced further from the enlargement so that it occurs at the root of the stem. Thus, at the rounded corner 12 the stem 56 is of intermediate thickness.

In this arrangement the greatest static squeeze sealing the primer occurs displaced from the zone of greatest diametric squeeze in response to the development of the pressure.

In the embodiments of FIGS. 4 and 5 compressive reformation of the plastic material renders the material in the stem, particularly at the enlargement increased in tensile strength which makes a tighter seal.

This all makes for improved sealing engagement particularly when the propellant is ignited. The thin neck at 8, 48, or 58 is most responsive to increase in gas pressure in increasing the sealing engagement adjacent the primer radius 12. At the same time it allows the end ring to contract desirably. Moreover, the inner surface at and around the lip 9 or flap 49 is also responsive for a pressure-responsive increase in sealing engagement axially. At the same time the axial extension of the primer inwardly along the axial length of the primer opening 4 is such that the end sealing ring at 7 or 47 and its lip 9 or flap 49 are maintained snugly against the inner extremity of the primer by reason of axial and circumferential tension thus produced in the stem.

FIGURE 6 shows another way of forming the first stage of the stem at the primer hole and shows that, although in the foregoing embodiments this was done before the metal head is assembled, the grooved plastic head structure can be made with the metal head 13 in place. Plastic body 61 has a sidewall 62 and an integral base 63 having an opening 64 through the head. In FIG. 6 the opening is formed to an inner reduction by the action of forming punch 71 indenting the base as shown to form in the shell of FIG. 7 groove 65 and also form stem 66 against a stepped pin 72. Reduced end 76 extends up into the bore 74 of the punch and is joined by taper 77 to pin portion 78, which is somewhat smaller than the diameter of the primer 10. A slight stem extension 67 is formed to extend beyond the inner extremity of the primer when emplaced as shown in FIG. 7. This is done in any suitable base confining die 79 where the radially confined assembly is held axially with the aid of any suitable backup means such as bunter 73, against the force of the annular indenting ridge 75 of the punch.

The final shape shown in FIG. 7 is made by forcing in a primer to finish the primer hole 164 and push up the plastic in the hole to form the enlarged end ring 167 connected at a very thin neck 68 to the rest of the stem at a bend somewhat sharper than the bend at neck 8 of the FIG. 2 embodiment. The end ring in tension overlaps the end of the primer with a snug fit and includes the inner lip 69 about primer flash hole 11.

In all embodiments, the plastic material in the stem when the primer is inserted, is under increasing tension toward the inner end, at which the stem is preferably made to increased undersize with respect to the external diameter of the primer. Thus, despite the projection of the end of the stem beyond the end of the primer at the flash hole, the primer mounting stem is resistant to undesired outward bulging. With an overlapping inner lip and/ or a thick projecting rim, the accompanying conical or cylindrical end surface at the aperture in the projecting end of the stern tends to minimize bulging and acts to increase the sealing pinch on the primer.

This invention has utility with shells of any suitable resinous plastic, but is especially applicable to those of the type disclosed in copending patent application Serial Nos. 135,569 and 171,729, filed September 1, 1961, and February 7, 1962, respectively, relating to crystalline polymers and rigidifiable polyolefins of which linear high density polyethylene is an example.

What is claimed is:

1. An ammunition cartridge case including a tubular sidewall and integral base formed of a resinous plastic material, a primer opening in said base, a circular groove in said base concentric with said primer opening, a stem of said resinous material surrounding said primer opening, said stem having an overall height extending above a primer positioned in said opening and having a lip projecting inwardly toward said primerin peripheral gas sealing contact therewith.

2. The cartridge case of claim 1 in which said lip has a thin outer edge and has a lower surface contacting said primer positioned at a height predetermined to place said stem in gas sealing tension when a primer is positioned in said primer opening.

3. The cartridge case of claim 2 in which said lip is connected to the rest of the stem by a thinned neck portion.

4. The cartridge case of claim 1 in which said stem has a thinned wall portion directly adjacent its juncture with said base.

5. A cartridge casing made from a plastic material including a tubular sidewall, a relatively thick base formed integral with the sidewall, a primer opening formed in said base, a circular groove formed in the interior of said base concentric with said primer opening, a stem formed in the interior of said base between said primer opening and said groove, a ring extending inwardly toward said primer opening formed integral with the upper end of said stem, said ring being joined to the I rest of said stern by a pressure sensitive thinned portion and having a thin outer edge operative to engage a primer positioned in said opening and form a seal around said primer.

References Cited by the Examiner UNITED STATES PATENTS SAMUEL FEINBERG, Primary Examiner. 

1. AN AMMUNITION CARTRIDGE CASE INCLUDING A TUBULAR SIDEWALL AND INTEGRAL BASE FORMED OF A RESINOUS PLASTIC MATERIAL, A PRIMER OPENING IN SAID BASE, A CIRCULAR GROOVE IN SAID BASE CONCENTRIC WITH SAID PRIMER OPENING, A STEM OF SAID RESINOUS MATERIAL SURROUNDING SAID PRIMER OPENING, SAID STEM HAVING AN OVERALL HEIGHT EXTENDING ABOVE A PRIMER POSITIONED IN SAID OPENING AND HAVING A LIP PROJECTING INWARDLY TOWARD SAID PRIMER IN PERIPHERAL GAS SEALING CONTACT THEREWITH. 